To usher in is to launch something new, or mark its beginning. Your habit of wearing a tuxedo every day just may usher in a new era of formal wear at school.
Use this phrase for something that seems to represent a new stage or time period. The very earliest commercial plane flights ushered in an age of regular air travel, and the UK leaving the European Union will usher in a new phase for the whole region. Sometimes this phrase is used to mean "announce an arrival," the way your school's departing principal might usher in his replacement, introducing her to the students. To usher is to guide or escort.